Magnetically operated relays are used for switching of electrical current, and typically have a wire coil which, when electrically energized, creates a magnetic field to move an armature which in turn drives a movable contact into connection with one or more fixed contacts to complete a circuit. Relays are highly reliable devices which have many uses, but verification of proper armature movement is desirable in certain critical applications such as military equipment, and where high voltages and currents are being switched.
For example, a type of relay called a high-voltage direct-current power contactor may be used for switching currents in excess of 1000 amperes at voltages of 200-300 volts or more. Heavy-duty switches of this type typically position the fixed and moving contacts in an air-free sealed enclosure or chamber which is evacuated to a high vacuum, or evacuated and backfilled with an insulating gas such as nitrogen. The objective is to minimize arcing and localized contact melting (which can result in unwanted welding of the fixed and movable contacts) as the contacts make or break during high-current switching. Sealing of the contacts also isolates them from any corrosive or otherwise adverse external environment which might degrade conductivity of the contacts.
Preferably, all of the moving components of this type of relay or contactor are within the sealed chamber to eliminate need for a bellows or similar device for transmitting movement from the outside into the sealed environment. This configuration, however, prevents use of a simple external motion sensor which could be used to verify correct positioning of the armature (and hence of the moving contact or contacts). It is also desirable to isolate the motion sensor both electrically and mechanically from the high-voltage environment within the sealed enclosure or chamber.
This invention meets these objectives by providing a magnetically actuated armature-position sensor which can be mounted as a module on the exterior of the switching relay or contactor. The sensor incorporates a simple low-power on-off reed switch to provide an electrical indication of armature position. No penetration of the high-vacuum or backfilled sealed contact chamber is needed, and the sensor is readily adapted to use on a variety of existing relay or contactor designs.